What is Calcium?
Calcium is silvery white solid at room temperature and pressure. It is located
on the left side of the periodic table, near the other alkali and alkaline earth
metals. Calcium and its compounds are used for cement and plaster in building applications, in water treatment, and in the chemical industry.
Calcium’s Place in the Periodic Table
Calcium’s name is derived from the Latin word “calx,” meaning “lime.” This stems from the fact that lime (calcium oxide) is mainly made of calcium. Calcium is the third element in Group 2 of the periodic table, appearing after
magnesium. Elements in Group 2 are referred to as the alkaline earth metals.
Alkaline earth metals are called so because they form alkaline (basic) solutions when they react with water (by forming hydroxides). The word “earth” is included as part of the description given to their oxides. “Earth” is an old term used by early chemists to describe nonmetallic compounds that are not soluble in water and are poor conductors of heat, which describes the oxides of the alkaline earth metals.
- Atomic number: 20
- Symbol: Ca
- Group: 2
- Period: 4
- Number of Protons: 20
- Number of Electrons: 20
- Number of Neutrons [in most abundant or naturally occurring isotope]: 20
- Atomic radius: 180 pm
- Atomic mass: 40.078
- Number of Isotopes: 6
Properties of Calcium
At room temperature elemental calcium is a soft (easily scratched), silvery white solid. It corrodes rapidly in air and reacts with water. It also reacts vigorously with acids. As you know, calcium is an integral part to our bodies, so it is not surprising that its compounds are non-toxic to living organisms. However, calcium metal, because it reacts so violently with water, causes severe irritation when it comes into contact with moist parts of the body (e.g. mouth, esophagus, stomach).
Calcium does not occur as a free element in nature (because it is so reactive), but it can be found in many minerals, like limestone rock. It is also found within “hard” water. Calcium is classified as a solid and metal. Like most metals, calcium is a relatively good conductor of heat and electricity.
At room temperature and pressure, calcium exists as a ductile silvery white metal that can be easily cut or scratched. You can actually cut calcium metal with a knife (though it’s not a very easy task!)
- Melting Point: 842 °C = 1548 °F = 1115 K
- Boiling Point: 1484 °C = 2703 °F = 1757 K
- Density: 1.54 g cm-3
- Phase at Room Temperature: solid
Calcium is a very reactive metal due to its two valence electrons. It is inclined to donate those electrons, forming a chemical bond, in order to achieve a full octet. When it comes in contact with air, it corrodes (or tarnishes) to form a dark calcium oxide (CaO) and nitride (Ca3N2) coating (which prevents it from further corrosion). It can also be burned or combusted in air which results in a very bright light and a nitride product. Calcium reacts easily with water and acids to form various compounds as well (e.g. CaCl2 and Ca(NO3)2). Calcium is a good conductor of electricity because it has metallic bonding which allows the delocalized electrons (those from the outer shell) to flow freely from atom to atom, conducting electricity. It is a poorer conductor by volume compared to copper or aluminum but actually a better conductor by mass due to its very low density. Copper and aluminum are some of the best conductors out there, so that’s saying something!
- Oxidation States: 2
- Specific Heat: 631 J/kg*K
- Electronegativity: 1 (Pauling scale)
- Heat of Fusion: 8.54 kJ/mol
- Heat of Vaporization: 155 kJ/mol
- Electron Configuration: [Ar] 4s2
Calcium is unique because naturally-occurring calcium is actually composed of six essentially stable isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca, and 48Ca. These isotopes have varying natural abundances: 40Ca (96.941%), 42Ca (0.647%), 43Ca (0.135%), 44Ca (2.086%), 46Ca (0.004%), 48Ca (0.187%). 48Ca is technically not stable but for practical purposes is considered stable due to its extremely long half-life: 4.3×1019 years. Approximately 13 other isotopes of calcium exist with relatively short half-lives.
Alloys and Allotropes
Calcium alloys are used in large-scale manufacturing processes (mostly for batteries and other electrical components). The main advantage of these calcium alloys is their energy transfer capability; they can conduct electricity very efficiently. Lead calcium alloy, lead calcium tin alloy, and magnesium calcium alloy are the main alloys used in these industries. Calcium aluminum alloy and calcium silicon alloy are less commonly used alloys. In particular, calcium alloys are known for their use in car batteries. Since the 1980s they have been used to produce longer-lasting car batteries that can be recharged and discharged many times in their lifetimes.
No allotropes of calcium exist.
Interesting Facts about Calcium
- Caves in limestone rock are formed due to the continuous exposure of the limestone to acidic water (the water is slightly acidic because it contains dissolved carbon dioxide, forming bicarbonate). The acidic water dissolves the limestone over time, forming a cave.
- Lime was prepared from limestone and used as a building material as early as 7000 BC. The Romans used it as early as the 1st century as a building and sculpture material.
- The Egyptians built their pyramids using limestone blocks, and later on they used gypsum to hold the blocks together.
- Have you ever heard the phrase “to be in the limelight?” Because lime produces such a bright light when it is burned, it was used to light stages in theaters during the 1800s until electricity became widely available. From this, talk of the “limelight” was born.
- Calcium carbonate deposits are found all over the Earth’s surface as the fossilized remains of past marine life.
Occurrence and Abundance of Calcium
Calcium is essential for life, as it forms the teeth and other bones in our bodies in the form of calcium phosphate (Ca3(PO4)2), calcium fluoride (CaF2), and calcium carbonate (CaCO3). Calcium aids in blood clotting and muscle contraction. Calcium ions are also the most important messengers used by plant and animal cells for cell communication within an organism. The average human body contains approximately 1 kilogram (~2.2 pounds) of calcium, which equates to a 1.4% abundance, and makes it the most abundant metal in the human body. In fact, a lack of calcium results in a condition known as osteoporosis where the bones become extremely porous and easy to fracture. This condition is most common in older women. An excess of calcium can lead to kidney stones. We consume calcium in the form of milk and other dairy products, leafy green vegetables, fish, nuts, and seeds. Calcium is also present in egg shells, coral, many soils, and seawater (0.00042% abundance in oceans).
Calcium is the fifth most abundant element and third most abundant metal in the Earth’s crust with an abundance of approximately 5%. While it is not found in its pure form in nature, it does exist as part of several minerals including limestone (calcium carbonate), gypsum (calcium sulfate), fluorite (calcium fluoride), and apatite (calcium chloro- or fluoro-phosphate). “Hard” water contains calcium bicarbonate, which form stalactites and stalagmites in caves. In the universe overall, calcium has an abundance of 0.007%. The top producers of calcium are China, the United States of America, and India. Calcium is commercially produced from salt calcium chloride (CaCl2) and from limestone (CaCO3).
Uses of Calcium
Most Notable Uses in General
Aside from its use in alloys, pure calcium does not have many general uses due to its high reactivity. One main use of pure calcium draws from its quality to burn brightly. Calcium is used in fireworks to deepen the colors, and calcium salts are responsible for any orange fireworks that you see. It is also used as a deoxidizer (removes oxygen) in the production of steel.
Most Notable Uses in Science
Calcium is used as a reducing agent (it gets oxidized) in the production of other metals like thorium and uranium (which is critical for nuclear energy applications).
Discovery of Calcium
Though calcium compounds have been known and used for millennia (as a building material and plaster), it wasn’t until 1787 that Antoine Lavoisier suspected that lime (a mixture of calcium oxides and hydroxides) may contain a fundamental element. However, he was unsuccessful in further reducing it to pure calcium. In London in 1808, Humphry Davy first isolated pure calcium (and magnesium, strontium, and barium). His method involved producing calcium mercury and then distilling off the mercury to leave calcium metal. However, this method is not suitable for commercial production, and a commercial production method was not established until over a century a:er calcium’s initial discovery.
Calcium in the Future
Opportunities for calcium use in the future exist mostly for limestone, as many efforts are still underway to manipulate its physical properties and expand its use.